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Author

Karim Kassam

Date of Award

1996

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Supervisor

J. Warkentin

Abstract

Carbocyclic and heterocyclic compounds are ubiquitous in nature. Therefore, the discovery and development of new ring forming reactions are of paramount interest to synthetic organic chemists. Recently, the intramolecular cyclization of reactive intermediates, such as anions, cations, and radicals have provided a number of new methods by which known and novel ring systems can be constructed. Cyclizations involving tandem, or multiple sequences have gained considerable popularity due to their high overall efficiency and remarkable speed by which these processes can yield complex polycyclic ring systems.

Carbenes are another interesting class of reactive intermediates which undergo characteristic reactions. The cyclization reactions of carbenes have not been studied to a significant extent In particular, me work described in this thesis outlines the only study of the intramolecular cydization of dioxycarbenes onto a tethered alkyne moiety.

The first section of this dissertation details the development of a convenient new class of thermal dioxycarbene precursors, dioxyoxadiazolines I, which display many significant advantages over previously used sources of dioxycarbenes D.

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The second section of this dissertation details the use of dioxyoxadiazolines possessing a tethered triple bond for the thermal generation of dioxycarbenes III which are capable of intramolecular cyclization. It was found that the cyclization of a dioxycarbene onto a tethered triple bond results in the regioselective generation, of another reactive intermediate, a 3,3-dioxyvinylcarbene (IV or V, depending on the nature of R'), which can undergo a number of interesting intermolecular reactions. This approach leads to the rapid construction of some interesting and rather complex polycyclic heterocyles which are, in many cases, obtained with high regioselectivity and sometimes even high stereoselectivity.

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The results described in this thesis mark the discovery and development of a new synthetic methodology which may, by appropriate choice of the starting material, provide a valuable tool for the rapid and selective synthesis of a number of heterocyclic ring systems.

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